This invention relates to a solar engine in which thermal energy from the sun is converted directly to mechanical motion, without intermediate storage of the thermal energy. More particularly, it relates to such a solar engine in which rays of the sun are concentrated and successively directed to a plurality of elements which convert energy from the concentrated rays to mechanical motion.
There has long been theoretical interest in engines which take the thermal energy required for their operation from the sun's rays. Heat engines offer a means for direct utilization of the energy of the sun since the sun's radiant energy can be focused onto a boiler or other light absorbing element to provide the heat source for the engine. For example, on a large scale, mirrors could be used to focus the energy on a boiler for a turbine system. Such a system, however, requires the transmission of heat from a collecting device into an expansion chamber. Heat will invariably by lost during such a transfer with a resultant decrease in working fluid temperature. Since engine efficiency increases with fluid operating temperature, any such decrease in fluid temperature will result in lower engine efficiency.
One solution to the problem of energy loss during heat transfer is to effect the heat collection within the work space of the engine by utilizing transparent walls or cylinder heads and incorporating an absorbing element within the work space. High temperatures and minimum energy loss can be obtained in this manner since the transparent wall and work space can be well insulated, the radiation can be sharply focused on a small work space, and efficient absorbing structures can be utilized. One such thermal engine has been described in U.S. Pat. No. 3,117,414.
One major drawback of many thermal engines, including the solar engine just described, is the inability to efficiently utilize the energy available from the heat source. This is especially true with cyclical engines which require that the energy be applied at the proper instant of the cycle and for the proper duration of the cycle with little waste of energy during those portions of the cycle not requiring heat input. For example, the Carnot cycle demands that heat be extracted from the heat source only during the isothermal expansion portion of the cycle; no heat is extracted from the source during the subsequent adiabatic expansion, isothermal compression or adiabatic compression portions completing the cycle. Achieving this cyclical interrupted heat flow is difficult and inefficient if the heat resides in a fluid. A means of achieving heat transfer from the heat source to the working fluid during only a portion of the cycle requires some transfer of working fluid or heat source fluid which must be controlled by valves or other mechanical means. Such controls can themselves have substantial energy requirements, thus detracting from overall engine efficiency.